Method for characterizing activation of an anatomical tissue subjected to contraction

Abstract

This disclosure relates to a method for characterizing activation of an anatomical tissue subjected to contraction, aiming at providing a characterization of the contraction itself in a quantitative manner which is accurate and repeatable. The invention proposes an analysis of the activation of the anatomical structure based on instantaneous spectral contents of an activity signal from which an identification of peaks of dominant frequency characterizing the contraction throughout the anatomical tissue results. An evolution of a spatial distribution of peaks of dominant frequency throughout the anatomical tissue over time can also be monitored. The disclosure finds particular advantageous applications in provision of a mapping of activation of the anatomical tissue in order to identify a possible dysfunction, such as an arrhythmia in a cardiac tissue.

1 . Method for characterizing activation of an anatomical tissue subjected to contraction, the method comprising:
 acquiring an activation signal representative of an electrical activity of the anatomical tissue with respect to time, and determining an activation time period including a single electrical pulse corresponding to the contraction,   in synchronization with acquisition of the activation signal, acquiring consecutive images of the anatomical tissue at a high cadence over the activation time period, and segmenting each image of the anatomical tissue in a plurality of pixels,   for each pixel, determining an activity signal representative of a mechanical activity of the pixel with respect to time between consecutive images over the activation time period,   for each pixel, dividing the activation time period in a plurality of elementary time windows, calculating a spectral content of the activity signal in each elementary time window, determining a dominant frequency in each elementary time window and identifying a peak of dominant frequency in the activation time period, the peak of dominant frequency characterizing the contraction.   
     
     
         2 . Method according to  claim 1 , further comprising:
 for each pixel, determining a contraction timing corresponding to a pixel peak time at which the peak of dominant frequency occurs from an initial time of the activation time period,   displaying a pattern of contraction by attributing a display parameter to the contraction timing of each pixel.   
     
     
         3 . Method according to  claim 1 , wherein identifying the peak of dominant frequency in the activation time period comprises:
 determining a tissue peak time at which peaks of dominant frequency are reached in a largest number of pixels comprised in the tissue,   refining the activation time period with respect to the tissue peak time, and   defining the peak of dominant frequency for each pixel as a first local maximum of dominant frequency within the refined activation time period.   
     
     
         4 . Method according to  claim 3 , wherein refining the activation time period comprises beginning the activation time period at a time interval before the tissue peak time. 
     
     
         5 . Method according to  claim 1 , wherein determining the activity signal comprises measuring a mechanical parameter representative of the mechanical activity of each pixel on each consecutive images. 
     
     
         6 . Method according to  claim 5 , wherein the mechanical parameter is chosen among a displacement of the pixel and a strain of the pixel. 
     
     
         7 . Method according to  claim 1 , wherein the high cadence is N images per second and the activation time period Ta is divided in successive elementary time windows Tf such that Tf is between Ta/3 and Ta/12 and two successive elementary time windows are shifted of at most 0.5*N·Tf images, with one another, N being greater than or equal to 500 images. 
     
     
         8 . Method according to  claim 1 , wherein calculating the spectral content of the activity signal in each elementary time window is performed by implementing Short Time Fourier transform. 
     
     
         9 . Method according to  claim 1 , wherein acquiring images is performed by ultrasound modality, images of a plane in tissue thickness being acquired. 
     
     
         10 . Method according to  claim 9 , wherein the ultrasound modality is implemented in electromechanical wave imaging. 
     
     
         11 . Method according to  claim 9 , wherein acquiring images is performed by an intracorporeal ultrasound configured to emit an ultrasound signal and to receive echoes of a reflected signal. 
     
     
         12 . The method according to  claim 1 , wherein the anatomical tissue is cardiac tissue. 
     
     
         13 . Method according to  claim 12 , wherein refining the activation time period comprises beginning the activation time period at a time interval corresponding to a duration of isovolumetric contraction of the cardiac tissue. 
     
     
         14 . Method according to  claim 7 , wherein two successive elementary time windows are shifted of at most 0.5*N·Tf images, or 0.25*N·Tf images, or 0.1*N·Tf images, with one another, and wherein N≥1000 images, or N≥1500 images or N≥2000 images. 
     
     
         15 . The method according to  claim 7 , wherein the anatomical tissue is cardiac tissue and the Ta is between 30 ms and 120 ms.